Systems and Methods for Undercut Features on Injected Patterns

ABSTRACT

A method for creating undercut features in a wax pattern in an investment casting process is disclosed. The method comprises designing a tooling that includes a mold for an object with an aperture and a core corresponding in size and shape of the aperture. Then, the mold is used to injection mold a pattern for the object, wherein the pattern includes an opening corresponding to the aperture. Next, a plug from the core of the tooling is injection molded using the mold. The plug is press-fitted into the opening of the pattern and the opening of the pattern is sealed with the plug.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to and the benefit of U.S. provisional application No. 61/788,444 filed on Mar. 15, 2013, incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to the field of investment casting. Specifically, this disclosure relates to methods and systems to insert undercut features on injected patterns.

BACKGROUND

Investment casting is an industrial process based on lost-wax casting. Investment casting is one of the oldest known metal-forming techniques. During World War II, the increased demand for precisely dimensioned parts popularized the industrial use of investment casting. The production of an investment cast results in a ceramic casting vessel having an outer ceramic shell with an inside surface corresponding to the desired shape, and one or more ceramic cores positioned within the outer ceramic shell corresponding to the desired design.

The production of investment casting involves multiple steps. First, a master pattern is produced by a mold-maker using one of a wax, clay, wood, plastic, steel, or another material.

Next, a mold, also known as the master die, is made from the master pattern. The mold may be made from a low-melting-point metal, steel, or wood. If a steel pattern was created then a low-melting-point metal may be cast directly from the master pattern. Alternatively, the master pattern is machined directly into steel.

Thereafter, wax patterns are produced using the mold. The wax pattern may be created using wax, plastic and frozen mercury. The wax may be poured into the mold and swished around until an even coating with a desired thickness is reached. Next, the wax pattern is removed from the mold. Finally, the ceramic mold, known as the investment, is produced. The ceramic mold is the cast of the desired shape.

However, when wax patterns are produced using the mold, often undercut features need to be included in the wax pattern. An undercut feature of a part is one that projects back into the main body of the part. Some examples of undercuts include threads, certain snap features, blind openings, negative tapered features, locking tabs, pockets, and holes in sidewalls. Undercuts add complexity to the investment casting process. Some undercuts may prevent the wax or plastic part from being ejected from the mold properly. Therefore, additional methods, such as soluble wax cores and ceramic cores, or complex, collapsing tooling are employed to make undercut features in wax patterns. The methods using soluble wax cores involve using a soluble wax pattern designed with reference to an undercut feature. The soluble wax pattern is injected using an additional wax injection tool. Further, additional chemical processing is required to remove soluble wax. The methods using ceramic cores involve a ceramic core pattern designed with reference to an undercut feature. The ceramic cores remain part of the wax pattern and are removed after the pattern is cast.

Therefore, the methods to produce undercut features add extra processing operations, which increase the cost from the tooling to the casting process. Therefore, improved systems and methods are required for creating undercut features in wax and plastic injection molds that require fewer steps and are more economical than the methods described above.

SUMMARY

The present disclosure relates to creating undercut features for wax patterns used in investment casting, and instrumentation and methods for preparation of these patterns. The primary examples described herein illustrate how this concept is applied to creating a tibial baseplate implant, but this concept applies equally to other objects with undercuts, such as threads, snap features, blind openings, negative tapered features, locking tabs, pockets, and holes in sidewalls. The disclosed method involves designing a tooling. The tooling includes a mold for an object with an aperture and a core corresponding in size and shape to the aperture. The method involves using the mold to injection mold a pattern for the object, wherein the pattern includes an opening corresponding to the aperture. Next, the mold is used to injection mold a plug from the core of the tooling, press fit the plug into the opening of the pattern, and seal the opening of the pattern with the plug.

Further, the present disclosure discloses a system for creating undercut features in a wax pattern. The system comprises a designing means to design a tooling, wherein the tooling includes a mold for an object with an aperture and a core corresponding in size and shape of the aperture. The system further comprises a molding means to injection mold a pattern for the object and a plug from the core of the tooling, wherein the pattern including an opening corresponding to the aperture. In addition, the system includes a means to press-fit the plug into the opening of the pattern. Finally, the system includes a sealing means to seal the opening of the pattern with the plug.

The present disclosure also discloses a tool for creating undercut features in a wax pattern in investment casting process. The tool comprises a mold for an object with an aperture for forming a pattern for the object, wherein the pattern includes an opening corresponding to the aperture. The tool further comprises a core corresponding in size and shape to the aperture for forming a plug, wherein the plug is press-fit into the opening of the pattern to seal the opening of the pattern.

The disclosed method eliminates secondary manufacturing operations and simplifies tooling design to reduce the overall manufacturing costs associated with undercut features. Further, the disclosed methods and systems enable better design compliance, are repeatable and are simple as compared to earlier known methods.

Those of skill in the art will recognize that the following description is merely illustrative of the principles of the disclosure, which may be applied in various ways to provide many different alternative embodiments and may be applicable outside the fields of surgery or medical devices. While the present disclosure is made in the context of a tibial baseplate implant for the purposes of illustrating the concepts of the process, it is contemplated that the present process and/or variations thereof may be suited to other uses, such as to support other joints in the human body and to stabilize bone fractures. Moreover, the implants, instrumentation, and methods set forth herein may be used in open, percutaneous, and/or minimally invasive procedures. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present disclosure will now be discussed with reference to the appended drawings. It will be appreciated that these drawings depict only typical examples of the present disclosure and are, therefore, not to be considered limiting of its scope.

FIG. 1A is a perspective view of a tibial baseplate implant according to an example embodiment of present disclosure;

FIG. 1B is a top view of the tibial baseplate implant of FIG. 1A;

FIG. 1C is a side view of the tibial baseplate implant of FIG. 1A, with a partial cutaway to show a blind bore;

FIG. 2 is a flowchart illustrating a method for creating undercut features in wax and plastic injection molds, according to one aspect of the present disclosure;

FIG. 3A is a side view of a tooling for the implant of FIG. 1, with dashed lines indicating interior features;

FIG. 3B is a top down view of the tooling of FIG. 3A, with dashed lines indicating interior features;

FIG. 3C is a cross-sectional view of the tooling of FIG. 3B, taken along line 3C-3C in FIG. 3B;

FIG. 3D is a detail view of an area “3D” in FIG. 3C;

FIG. 3E is a detail view of an area “3E” in FIG. 3C;

FIG. 4A is a tibial baseplate pattern and two plugs created from the tooling of FIG. 3A;

FIG. 4B is an enlarged partial cross-section of the tibial baseplate pattern of FIG. 4A, with a plug inserted in an opening;

FIG. 5 shows a portion of a knee with an inserted tibial baseplate, the tibial baseplate created from the tooling of FIG. 3A, according to an example of the present disclosure;

FIG. 6A is a tooling for creating a locking tab, according to an example embodiment of present disclosure; and

FIG. 6B is a locking tab created from the tooling of FIG. 6A.

DETAILED DESCRIPTION

While certain embodiments are shown and described in detail below by way of illustration only, it will be clear to the person skilled in the art upon reading and understanding this disclosure that changes, modifications, and variations may be made and remain within the scope of the technology described herein. Further, while various features are grouped together in the embodiments for the purpose of streamlining the disclosure, it is appreciated that features from different embodiments may be combined to form additional embodiments that are all contemplated within the scope of the disclosed technology.

Not every feature of each embodiment is labeled in every figure where that embodiment appears, in order to keep the figures clear. Similar reference numbers (for example, those that are identical except for the first numeral) may be used to indicate similar features in different embodiments.

Any of the devices, toolings, and apparatuses described herein may be fabricated from metals, alloys, polymers, plastics, ceramics, waxes, woods, clays, plastics, glasses, composite materials, or combinations thereof, including but not limited to: PEEK, titanium, titanium alloys, commercially pure titanium grade 2, ASTM F67, Nitinol, cobalt chrome, stainless steel, UHMWPE, and biodegradable materials, among others. Different materials may be used within a single part. The implants disclosed herein may also encompass a variety of surface treatments or additives to encourage bony attachment, including but not limited to: porous coatings, hydroxyapatite, TCP, anti-microbial additives, analgesics, anti-inflammatories, BMP's, PMA material, bone growth promoting material, PLLA (poly-L-lactide), PGA (polyglycolide), TCP (tricalcium phosphate), demineralized bone, cancellous bone chips, etc. Any implant disclosed herein may include a radiographic marker for imaging purposes. Any implant disclosed herein may be colored, coded, or otherwise marked to make it easier for the surgeon to identify the type and size of the implant.

FIG. 1A shows a perspective view of a tibial baseplate implant 100 according to an example embodiment of present disclosure. The tibial baseplate implant 100 includes two undercut features: a first blind bore 102 and a second blind bore 104, which are recessed into a lower surface 106 of the tibial baseplate implant 100. FIG. 1B is a top view of the tibial baseplate implant 100 of FIG. 1A. FIG. 1C is a side view of the tibial baseplate implant of FIG. 1A. FIG. 1C shows additional details of the blind bore 104 in a partial cutaway 108. The blind bore 104 is an undercut feature circumscribing the bore. The blind bore 104 also includes a tapered sidewall 110. The undercut angle of the tapered sidewall 110 is illustrated by the extended dashed lines 112.

FIG. 2 is a flowchart illustrating a method 200 for creating undercut features in wax and plastic injection molds, according to one aspect of the present disclosure. The method 200 is explained in the context of creating undercut features in the tibial baseplate implant 100. FIGS. 3A-3E and 4A-4B illustrate the steps of the method 200 for creating the blind bores 102 and 104 in the tibial baseplate implant 100. FIG. 3A is a side view of a tooling for the implant of FIG. 1, with dashed lines indicating interior features. FIG. 3B is a top-down view of the tooling of FIG. 3A, with dashed lines indicating interior features. FIG. 3C is a cross-sectional view of the tooling of FIG. 3B, taken along the line 3C-3C in FIG. 3B. FIG. 3D is a detailed view of an area “3D” in FIG. 3C. FIG. 3E is a detailed view of an area “3E” in FIG. 3C. Further, FIG. 4A depicts a tibial baseplate pattern and two plugs created from the tooling of FIG. 4A. FIG. 4B is an enlarged partial cross-section of the tibial baseplate pattern of FIG. 4A, with a plug inserted in an opening.

At step 202, the method 200 involves designing a tooling. The tooling includes a mold for an object having an aperture. The tooling also includes a core corresponding in size and shape to the aperture. The tooling may be made from a master pattern produced by a mold-maker using one of a wax, clay, wood, plastic, steel, or another material. Further, the tooling may be made using a low-melting-point metal, steel, or wood. Moreover, the master pattern may be machined directly into steel to produce tooling.

In an example embodiment, the object may be the tibial baseplate implant 100 having blind bores 102 and 104. Accordingly, a tooling 300 is created corresponding to the tibial baseplate implant 100. The tooling 300 includes cores 302 and 304 on the side opposite of the openings of the blind bores 102 and 104. The cores 302 and 304 corresponding in size and shape to the blind bores 102 and 104.

Next at step 204, the method 200 involves using the tooling to injection mold a pattern for the object, such that the pattern includes an opening corresponding to the aperture. Injection molding involves injecting a material into a mold to produce patterns or parts. Injection molding may be performed using metals, glasses, elastomers, confections, and most commonly thermoplastic and thermosetting polymers. The material for the part is fed into a heated barrel, mixed, and forced into a mold cavity where it cools and hardens to the configuration of the cavity.

In the example embodiment, during injection molding, the cores 302 and 304 create the undercut surfaces corresponding to the blind bores 102 and 104, while allowing the wax pattern to be pulled from the tooling 300. The result is a tibial baseplate pattern 400 with apertures 402 and 404 extending completely through the tibial baseplate pattern 400.

At step 206, using the tooling to injection mold a plug from the core of the tooling. Accordingly, in the example embodiment, plugs 306 and 308 are created to fill in the apertures 402 and 404 in order to create the radius geometry on the bottom of the design. The plugs 306 and 308 may also be referred to as inserts. A split line 310 for the two plugs 306 and 308 occurs on the tangency of the radius, normal to the feature opening.

At step 208, the method 200 involves press-fitting the plug into the opening of the pattern. Referring to FIG. 4A, the tooling 300 is injected to create the tibial baseplate pattern 400 and the two plugs 306 and 308. A partial cut away 406 shows details of the aperture 404. FIG. 4B shows an enlarged view of the partial cut away 406. Immediately following pattern removal, the plugs 306 and 308 are pressed into the apertures 402 and 404 on the tibial baseplate pattern 400 until they are seated, as seen in FIG. 4B.

Finally, at step 210, the method 200 involves sealing the opening of the pattern with the plug. Accordingly, in the example embodiment, the plugs 306 and 308 are made slightly larger and are press-fit into place to keep the plugs in place and create a precise seal. For example, the plugs 306 and 308 are 0.001″ larger than the apertures 402 and 404. The aperture 404 may be 0.474″ long while the plug 308 may be 0.475″ long. To complete the casting process, the tibial baseplate pattern 400 with the attached plugs 306 and 308 is cast. The finished tibial baseplate implant 100 will include the blind bores 102 and 104 with the undercut tapered sidewalls 110.

The finished tibial baseplate implant 100 may be implanted in a proximal tibia 502 as shown in FIG. 5. The lower surface 106 of the tibial baseplate implant 100 rests on a tibial plateau 504. Further, pegs may be inserted in the bores 102 and 104 to secure the tibial baseplate implant 100 in proper place in the bone.

It is appreciated that the systems and methods disclosed herein may be used to create various patterns and objects with blind openings, negative tapered features, undercut features such as locking tabs, and pockets. FIG. 6A shows a tooling 600 for creating a locking tab feature according to an exemplary embodiment of the present disclosure. FIG. 6B is a locking tab 602 created using the tooling 600 and the method 200 describe above.

It will be appreciated that any of the designs, methods, and concepts contemplated herein can be mixed and matched to form alternate embodiments. These devices and methods may be used to create other tooling, patterns, and objects.

It should be understood that the present components, systems, kits, apparatuses, and methods are not intended to be limited to the particular forms disclosed. Rather, they are intended to include all modifications, equivalents, and alternatives falling within the scope of the claims. They are further intended to include embodiments that may be formed by combining features from the disclosed embodiments, and variants thereof.

The claims are not to be interpreted as including means-plus- or step-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase(s) “means for” or “step for,” respectively.

The term “coupled” is defined as connected, although not necessarily directly, and not necessarily mechanically.

The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and/or the specification may mean “one,” but it is also consistent with the meaning of “one or more” or “at least one.” The term “about” means, in general, the stated value plus or minus 5%. The use of the term “or” in the claims is used to mean “and/or” unless explicitly indicated to refer to alternatives only or the alternative are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and “and/or.”

The terms “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as “has” and “having”), “include” (and any form of include, such as “includes” and “including”), and “contain” (and any form of contain, such as “contains” and “containing”) are open-ended linking verbs. As a result, a method or device that “comprises,” “has,” “includes,” or “contains,” C/D one or more steps or elements, possesses those one or more steps or elements, but is not limited to possessing only those one or more elements. Likewise, a step of a method or an element of a device that “comprises,” “has,” “includes,” or “contains” one or more features, possesses those one or more features, but is not limited to possessing only those one or more features. Furthermore, a device or structure that is configured in a certain way is configured in at least that way, but may also be configured in ways that are not listed.

The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. It is appreciated that various features of the above-described examples can be mixed and matched to form a variety of other alternatives. As such, the described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be included within their scope. 

What is claimed is:
 1. A method for creating undercut features in a wax pattern in an investment casting process, the method comprising: designing a tooling, wherein the tooling includes a mold for an object having an aperture and wherein the tooling includes a core corresponding in size and shape of the aperture; using the mold to injection mold a pattern for the object, wherein the pattern includes an opening corresponding to the aperture; using the mold to injection mold a plug from the core of the tooling; press-fitting the plug into the opening of the pattern; and sealing the opening of the pattern with the plug.
 2. The method of claim 1, wherein the wax pattern is created using one of wax, plastic, and frozen mercury.
 3. The method of claim 1, wherein the undercut feature includes at least one of a thread, a snap feature, a blind opening, a negative tapered feature, a locking tab, a pocket, and a hole in side walls.
 4. The method of claim 1, wherein the plug is larger than the opening.
 5. The method of claim 4, wherein the edges of the plug are 0.001″ larger than corresponding edges of the opening.
 6. The method of claim 1, further comprising casting the pattern obtained after sealing the opening of the pattern to obtain a cast shaped like the object.
 7. The method of claim 1, wherein the object is a tibial baseplate implant.
 8. A system for creating undercut features in a wax pattern, the system comprising: a designing means to design a tooling, wherein the tooling includes a mold for an object with an aperture, and wherein the tooling includes a core corresponding in size and shape of the aperture; a molding means to injection mold a pattern for the object and a plug from the core of the tooling, wherein the pattern includes an opening corresponding to the aperture; a means to press-fit the plug into the opening of the pattern; and a sealing means to seal the opening of the pattern with the plug.
 9. The system of claim 8, wherein the wax pattern is created using one of wax, plastic, and frozen mercury.
 10. The system of claim 8, wherein the undercut feature includes at least one of a thread, a snap feature, a blind opening, a negative tapered feature, a locking tab, a pocket, and a hole in side walls.
 11. The system of claim 8, wherein the plug is larger than the opening.
 12. The system of claim 11, wherein the edges of the plug are 0.001″ larger than corresponding edges of the opening.
 13. The system of claim 8, further comprising casting the pattern obtained after sealing the opening of the pattern to obtain a cast shaped like the object.
 14. The system of claim 8, wherein the object is a tibial baseplate implant.
 15. A tool for creating undercut features in a wax pattern in investment casting process, the tool comprising: a mold for an object with an aperture for forming a pattern for the object, wherein the pattern includes an opening corresponding of the aperture; and a core corresponding in size and shape to the aperture for forming a plug, wherein the plug is press-fit into the opening of the pattern to seal the opening of the pattern.
 16. The tool of claim 15, wherein the wax pattern is created using one of wax, plastic, and frozen mercury.
 17. The tool of claim 15, wherein the undercut feature includes at least one of a thread, a snap feature, a blind opening, a negative tapered feature, a locking tab, a pocket, and a hole in side walls.
 18. The tool of claim 15, wherein the plug is larger than the opening, wherein the edges of the plug are 0.001″ larger than corresponding edges of the opening.
 19. The tool of claim 15, further comprising casting the pattern obtained after sealing the opening of the pattern to obtain a cast shaped like the object.
 20. The tool of claim 15, wherein the object is a tibial baseplate implant. 